Handbook of air conditioning and refrigeration / Shan K

where Psy � each air system total power input to the fan motors, hp (kW)
� volume flow rate of air system at design conditions, cfm (L/s)
V˙ s,d
For variable-air-volume (VAV) system: nameplate fan motor power is 0.0017 hp/cfm (0.0027 W
per L/s); when supply volume flow � 20,000 cfm (9440 L/s), allowable nameplate fan motor
power is 0.0015 hp/cfm (W per L/s). That is:
P sy
V˙ s,d
P sy
V˙ s, d
P sy can be calculated as
where �p sy,d � system total pressure loss at design conditions, in. WC (Pa)
� f,d, � d,d, � m,d � fan total efficiency, drive efficiency, and motor efficiency at design conditions
(17.24b)
(17.25a)
Substituting Eq. (17.25a) into Eq. (17.24), for constant-volume systems, the system total pressure
loss is
�p sy
� f,d� d,d� m,d
�p sy
� f,d� d,d� m,d
For VAV systems, the system total pressure loss is
�p sy
� f,d� d,d� m,d
�p sy
� f,d� d,d� m,d
In Eq. (17.24), temperature ratio can be calculated as:
Temperature ratio �
Pressure credit, in hp (kW), can be calculated as:
Tr, set � Ts,d 20
Pressure credit �
P sy �
Relief fan credit, in hp (kW), can be calculated as:
�p sy,dV˙ s,d
6350� f,d� d,d� m,d
� 7.6 in. WC (Pa) when V˙ s,d � 20,000 cfm
� 7.0 in. WC (Pa) when V˙ s,d � 20,000 cfm
� 10.8 in. WC (Pa) when V˙ s,d � 20,000 cfm
� 9.5 in. WC (Pa) when V˙ s,d � 20,000 cfm
� V˙ s,d(�pfil � 1.0)
n�1
3718
�
Relief fan credit � Pr, f �1 � 1 � V˙
r, f
V˙ � s,d
AIR SYSTEMS: AIR DUCT DESIGN 17.11
� 0.0017 hp / cfm (0.0027 W�s / L) when V˙ s,d � 20,000 cfm
� 0.0015 hp / cfm (0.0024 W�s / L) when V˙ s,d � 20,000 cfm
� V˙ s,d�pHR m�1
3718
(17.25b)
(17.25c)
(17.26)
(17.27a)
(17.27b)